Many chemical and physical reaction processes such as hydrogenation, oxidation, polymerization, coating, filtering, adsorption, and the like are carried out in fluidized beds. A fluidized bed, briefly, consists of a mass of solid particulate fluidizable material in which the individual particles are neutrally levitated free of each other by fluid drag forces such that the mass or fluidized bed possesses certain characteristics of a liquid. Like a liquid, it will flow or pour freely, there is a hydrostatic pressure head, its surface seeks a constant level, it will permit the immersion of objects and will support relatively buoyant objects. A fluidized bed is conventionally produced by directing a flow of a fluid through a porous or perforated plate or membrane, underlying the particulate mass, at a rate sufficient to support the individual particles against the force of gravity. Conditions at the minimum fluidization flow, i.e., the incipient fluidization point, are dependent on many parameters including particle size, particle density, etc. Any increase in fluid flow beyond the incipient fluidization point causes an expansion of the fluidized bed to accommodate the increased fluid flow. Further increase of the gas velocity will produce a condition where the particles are then carried out of the apparatus, a condition otherwise known as entrainment.
Fluidized beds possess many desirable attributes, for example, they may be used to effect temperature control, heat transfer, catalytic reactions, and various chemical and physical reactions such as oxidation, reduction, drying, adsorption, polymerization, coating, diffusion, filtering and the like.
Numbers of workers have studied the influence of magnetization on the dynamics of gas fluidized solids wherein there is no net solids flow to or from the vessel, the so-called batch beds. An early account of this phenomena was reported by M. V. Filippov [Applied Magnetohydrodynamics, Trudy Instituta Fizika Akad. Nauk., Latviiskoi SSR 12: 215-236 (1960); Zhurnal Tekhnicheskoy Fiziki, 30 (9): 1081-1084 (1960); Izvestiya Akad. Nauk., Latviiskoi SSR, 12(173): 47-51 (1961); Izvestiya Akad. Nauk.: Latviiskoi SSR, 12: 52-54 (1961); and Aspects of Magnetohydrodynamics and Plazma Dynamics, Riga (1962), Izvestiya Akad. Nauk., Latviiskoi SSR, pp. 637 to 645]. Subsequent workers have reported on the influence that magnetization exerts on pulsations, heat transfer, structure, and other characteristics of magnetized and fluidized solids in batch beds. A review of some of this work is given by Bologa and Syutkin [Electron Obrab Mater, 1: 37-42 (1977)]. Ivanov and coworkers have described some benefits of using an applied magnetic field of fluidized ferromagnetic solids in the ammonia synthesis process [see British Pat. No. 1,148,513 and numerous publications by the same authors, e.g., Ivanov et al, Kinet. Kavel, 11(5): 1214-1219 (1970); Ivanov et al, Zhurnal Prikladnoi Khimii, 43, 2200-2204 (1970); Ivanov et al, Zhurnal Prikladnoi Khimii, 45: 248-252 (1972); Ivanov et al, Chemical Industry, 11; 856-858 (1974); Shumkov et al, Zhurnal Prikladnoi Khimii, 49 (11): 2406-2409 (1976)]. Various means for operating magnetic fields to stabilize the bed of magnetizable solids have been disclosed in U.S. Pat. Nos. 3,440,731; 3,439,899; 4,132,005 and 4,143,469 and Belgium Pat. No. 865,860 (published Oct. 11, 1978).
R. E. Rosensweig [Science, 204: 57-60 (1979), Ind. Eng. Chem. Fundam., 18 (3): 260-269 (1979) and U.S. Pat. Nos. 4,115,927 (now reissued as Re. 31,439 on Nov. 15, 1983), and 4,136,016 (now Re. 31,186, reissued Mar. 22, 1983), the entirety of all are incorporated by reference] reported on a number of features of magnetically stabilized fluidized magnetizable solids and a systematic interpretation of the phenomena. In these publications and patents, R. E. Rosenweig reported on the quiescent fluid-like state for the magnetically stabilized fluidized bed (MSB), particularly one which is totally free of bubbles or pulsations or backmixing when a uniform magnetic field is applied to a bed of magnetizable solids, approximately colinear with the direction of the fluidizing gas flow.
Others have reported the use of continuously flowing cocurrent or countercurrent magnetically stabilized fluidized beds with a variety of chemical reactions and adsorptive or absorptive processes. U.S. Pat. No. 4,127,987 to Coulaloglou et al, issued Feb. 3, 1981, relates to a process for continuous countercurrent contacting to absorb one species from a contacting fluid by use of at least one magnetically stabilized fluidized bed. Similarly, U.S. Pat. No. 4,292,171, issued Sept. 29, 1981 and U.S. Pat. No. 4,294,688 to Mayer, issued Oct. 31, 1981, disclose catalytic hydrocarbon conversion processes in which magnetizable particles with or without separate catalytic particles are passed countercurrent to the hydrocarbon feed to effect a chemical conversion. U.S. Pat. No. 4,319,892 to Waghorne et al, issued Mar. 16, 1982, and U.S. Pat. No. 4,319,893 to Hatch et al, issued Mar. 16, 1982, teach an adsorption process for the separation of hydrogen from feed gas or vapor which contains hydrogen in admixtures of one or more hydrocarbon components. Each process uses a set of vertically stacked magnetically stabilized fluidized beds to effectuate one or more steps in the adsorption-desorption process. The adsorbent passes through each of the MSBs in a direction countercurrent to its particular gas flow.
V. A. Naletova in an article entitled "Stabilization of Bubble-liquid Processes by an Electric Field" in Izvest. Akad. Nauk. SSR, Mekh, Zhio. Igaza, No. 4, pp. 5-12 (1982) (Trans. Plenum Press (1983) 491-7) discusses the stabilization of bubbles rising or sediments descending in stagnant liquids where either phase may be more polarizable. Analogous magnetic stabilization is also discussed.
However, none of the noted publications suggest the use of magnetizable fluid as a medium for stably fluidizing nonmagnetizable particles.
The use of ferrofluids as the medium in which particles having different densities are separated by their densities is disclosed in U.S. Pat. No. 3,951,785 to Kaiser et al, issued Apr. 20, 1976, and in U.S. Pat. No. 3,484,969 to Rosenweig, issued Dec. 16, 1969. Neither of these patents describe a process using ferrofluid as a fluidizing medium for nonmagnetizable particles.